Magnetic Resonance of Cardiac C13 Flux & Metabolism Rate

 描述(申请人提供)：心脏中的甘油三酯(TG)的中性脂库，曾经被认为是一个静态的，不活跃的未使用脂肪的储存库，最近被认为是一个动态的酯化长链脂肪酸(LCFA)池，不断地翻转提供LCFA作为PPAR-a核受体激活的配体，随后代谢酶表达的转录激活，以及线粒体？氧化的重要燃料来源。在肥胖或胰岛素抵抗的动物模型和人类中，心脏脂质动力学的失调与最终的心功能下降有关。因此，将改变的心脏TG动力学与收缩性能联系起来，对于作为潜在治疗靶点的预后指征和疾病机制的确定都有希望。我们的发现既阐明了心脏TG的这种动态性质，也阐明了啮齿动物心脏的动态模式13C核磁共振所观察到的来自~(13)C-LCFA的TG富集率的不同动力学成分。这些动力学对应于载体介导的心肌摄取或细胞内TG池内的周转。初步数据表明，两种主要的膳食LCFA富含血浆，棕榈酸和油酸，导致不同的甘油三酯周转率。这项拟议的研究利用这些发现来研究LCFA对完整大鼠和 小鼠心脏可能决定生理活性和潜在的脂毒性酰基中间体、神经酰胺和二酰甘油酯(DAG)的形成。脂质动力学将在TG合成酶和脂肪酶表达改变的模型中以及在饮食诱导的代谢应激过程中进行探索。重要的是，大鼠心脏的动态模式13C核磁共振将评估脂质动力学对西方饮食的反应，这与脂肪毒性和潜在的心肌病有关。我们假设：1)在油酸和棕榈酸酯的生理混合物中，通过13C核磁共振可以分辨出每种LCFA对TG合成和脂解的不同亲和力，这些动力学影响和定义了DAG和不同神经酰胺的形成；2)无论是富含油酸还是棕榈酸酯，正常和西方饮食，调节心脏脂质动力学，影响PPAR-a的激活和酰基衍生物的形成；3)在心脏甘油三酯的13C动力学谱中，可以区分改变的TG合成或脂解。目的1测定油酸和棕榈酸酯对大鼠心脏甘油三酯转化和低水平酰基衍生物形成的竞争亲和力。目的2测定富含高油酸或高棕榈酸的西方饮食对大鼠心脏甘油三酯转换率、LCFA氧化率、PPAR-a活性和酰基衍生物的影响，以及对心脏功能的潜在影响。目的3评价动态13C核磁共振技术检测转基因小鼠心脏甘油三酯合成酶和脂肪酶活性的特异性。总体目标是测试TG 13C富集率动力学对TG酯化和去酯化的特异性，并确定13C富集率的13C富集率作为在心肌病理性代谢应激期间产生脂毒性神经酰胺和DAG的脂质储存动力学改变的标志。

 DESCRIPTION (provided by applicant): The neutral lipid pool of triglyceride (TG) in the heart, once thought to be a static, inactive depot for unused fat, has more recently been recognized to instead be a dynamic pool of esterified long chain fatty acid (LCFA), constantly turning over to provide LCFA as both a ligand for nuclear receptor activation of PPAR-a, with subsequent transcriptional activation of metabolic enzyme expression, and a significant fuel-source for mitochondrial ß-oxidation. The dysregulation of cardiac lipid dynamics is associated with eventual decline in ventricular function in both animal models and humans with obesity or insulin resistance. Linking altered cardiac TG dynamics to contractile performance therefore holds promise for both prognostic indications and identification of disease mechanisms as potential therapeutic targets. Our findings have elucidated both this dynamic nature of cardiac TG and the distinct kinetic components of TG enrichment rates from 13C-LCFA, as observed by dynamic-mode 13C NMR of the rodent heart. These kinetics correspond to either carrier-mediated uptake into the cardiomyocyte or turnover within the intracellular TG pool. Preliminary data demonstrate that two primary dietary LCFA abundant in plasma, palmitate and oleate, induce different TG turnover rates. The proposed research exploits these findings to investigate LCFA effects on intracellular lipid uptake, storage, and utilization dynamics in the intact rat and mouse heart that may determine formation of physiologically active and potentially lipotoxic acyl intermediates, ceramides and diacylglyceride (DAG). Lipid dynamics will be explored in models of altered TG synthase and lipase expression and during diet-induced metabolic stress. Importantly, dynamic-mode 13C NMR of rat hearts will assess lipid dynamics in response to a Western diet that is associated with lipotoxicity and potentially cardiomyopathic. We hypothesize that: 1) Within a physiological mixture of oleate and palmitate, the different affinities of each LCFA for TG synthesis and lipolysis, can be discerned by 13C NMR and these dynamics influence and define formation of DAG and different ceramides; 2) Either oleate-rich or palmitate-rich, normal and Western diets, mediate cardiac lipid dynamics, affecting activation of PPAR-a and acyl-derivative formation; 3) altered TG synthesis or lipolysis can be distinguished within the 13C kinetic profile of TG in the heart. Aim 1 determines competing affinities of oleate and palmitate for TG turnover and low-level acyl derivative formation in rat hearts. Aim 2 determines TG turnover, LCFA oxidation rates, PPAR-a activation, and acyl-derivatives in rat hearts during a Western diet, enriched with either high oleate or high palmitate, and potential effects on cardiac function. Aim 3 assesses specificity of dynamic-mode 13C NMR for TG synthase and lipase activity in transgenic mouse hearts. The overall objectives are to test the specificity of TG 13C-enrichment kinetics for TG esterification and de-esterification and to identify 13C-enrichment kinetics of the 13C enrichment rates that serve as signatures for altered lipid storage dynamics that produce lipotoxic ceramides and DAG during cardiomyopathic metabolic stress.